Studies of Paramagnetic Lanthanide Complexes
Synthesis of [(C5Me5)2(THF)Ce]2(µ-η2:η2-N2), 2. In a glovebox,
[(C5Me5)2Ce][(µ-Ph)2BPh2] (136 mg, 0.16 mmol) was added to KC8
(37 mg, 0.27 mmol) in 10 mL of THF, and the mixture was stirred
for 2 h. The solution was centrifuged to remove white and black
solids, and the solvent was removed in vacuo. Toluene extraction
followed by centrifugation and removal of solvent from the
supernatant in vacuo left a dark red oil. Recrystallization from
298K
the LnZ3/K and LnZ2Z′/K reduction methods3-7 were applied
to cerium using Z ) (C5Me5)1- and (C5Me4H)1- and Z′ )
(BPh4)1-. This method was also applied to the praseodymium
analogs to obtain another pair of paramagnetic dinitrogen
complexes with low magnetic moments (4f2 Pr3+, µ ) 3.58
toluene gave dark red needles of 2 (60 mg, 74%). øM
) 1459
× 10-6 (cgs); µeff ) 1.9 µB. 1H NMR (C7D8) δ -0.46 (8H, THF),
-0.03 (8H, THF), 1.17 (60H, C5Me5). 13C NMR (C7D8) δ 4.3
(C5Me5), 22.0 (THF), 53.8 (THF), 159.4 (C5Me5). 15N NMR (C7D8)
δ 871 (fwhh 22 Hz20). Anal. Calcd for C48H76N2O2Ce2: Ce, 28.21.
Found: Ce, 27.7. IR (C6H6) 3667w, 3640w, 3034w, 2957s, 2907vs,
2856vs, 2725w, 2362w, 2342w, 2142w, 1552s, 1494w, 1440vs,
1378s, 1258w, 1189 m, 1058 m, 1023s, 973 m, 872w, 803 m, 730
9
µB ). With these data in hand for comparison, variable-
temperature 15N studies were conducted on the equilibrium
in eq 1.
m, 710 m, 676vs, 587s cm-1
.
Synthesis of [(C5Me5)2(THF)Pr]2(µ-η2:η2-N2), 3. Following the
procedure for 2, [(C5Me5)2Pr][(µ-Ph)2BPh2] (202 mg, 0.24 mmol)
was added to KC8 (43 mg, 0.31 mmol) in 10 mL of THF.
Recrystallization from toluene gave dark orange needles (103 mg,
85%). øM298K ) 4358 × 10-6 (cgs); µeff ) 3.2 µB. 1H NMR (C7D8)
δ 2.73 (C5Me5), THF resonances could not be located. 13C NMR
(C7D8) δ -10.21 (C5Me5), 210.9 (C5Me5), THF resonances could
not be located. 15N NMR (C7D8) δ 2231 (fwhh 93 Hz20). Anal.
Calcd for C48H76N2O2Pr2: Pr, 28.27. Found: Pr, 28.9. IR (THF)
3675w, 3640w, 2971s, 2907s, 2856s, 2725w, 2362w, 2343w,
1969w, 1660w, 1610w, 1567w, 1536w, 1598w, 1447 m, 1378w,
1312w, 1289w, 1239w, 1208 m, 1181 m, 1104 m, 1069vs, 1031
Experimental Section
The manipulations described below were performed under
nitrogen with the rigorous exclusion of air and water using Schlenk,
vacuum line, and glovebox techniques. [(C5Me5)2Ln][(µ-Ph)2BPh2]
(Ln) Ce, Pr),11 (C5Me5)2Sm,12 and KC813 were made according to
the literature. 15N2 was purchased from Cambridge Isotope Labo-
ratories and used as received. Hydrated lanthanide trichlorides were
desolvated with NH4Cl.14 C5Me5H was dried over molecular sieves
and degassed prior to use. C5Me4H2 was distilled onto molecular
sieves and degassed prior to use. KC5Me5 and KC5Me4H were
prepared by adding C5Me5H and C5Me4H2, respectively, to excess
potassium bis(trimethylsilyl)amide or potassium bis(dimethylphe-
nylsilyl)amide15 in toluene. Solvents were sparged with argon and
dried as previously described.15 Magnetic susceptibility was
determined according to the literature.16 NMR solvents were dried
over sodium potassium alloy, degassed, and vacuum-transferred
m, 988w, 911s, 733w, 714w, 664w cm-1
.
Synthesis of (C5Me4H)3Ce, 4. Similar to the method of
Schumann, et al.,21,22 CeCl3 (280 mg, 1.14 mmol) and KC5Me4H
(548 mg, 3.42 mmol) were combined in 100 mL of THF and
allowed to stir overnight. The solution was filtered, and the solvent
was removed from the solution in vacuo. Toluene extraction
followed by filtering and removal of the solvent in vacuo left a
1
before use. H and 13C NMR spectra were recorded on a Bruker
GN 500 MHz spectrometer. 15N NMR spectra were obtained with
Bruker GN 500 MHz and Bruker Advance 600 MHz spectrometers.
15N NMR spectra were measured using an external reference of
15N-formamide (δ -267.8 with respect to nitromethane at δ 0).17
Infrared spectra were recorded as thin films obtained from either
benzene or THF using an ASI ReactIR 1000 spectrometer.18
Elemental analyses were performed by complexometric titration.19
[(C5Me5)2Sm]2(µ-η2:η2-15N2), 1. A concentrated solution of (C5-
Me5)2Sm in ca. 1 mL of d8-toluene in a J-Young NMR tube was
degassed by three freeze-pump-thaw cycles and the solution was
exposed to 1 atm of 15N2. 15N NMR (C7D8) at 263 K, δ -117; 248
K, δ -125; 233 K, δ -135; 218 K, δ -146; 203 K, δ -161.
1
green powder (448 mg, 85%). H NMR (C6D6) δ -10.88 (18H,
C5Me4H), 7.82 (18H, C5Me4H), 33.56 (3H, C5Me4H). 13C NMR
(C6D6) δ -11.6 (C5Me5H), 15.9 (C5Me4H), 158.9 (C5Me4H), 176.8
(C5Me4H), 198.4 (C5Me4H). Anal. Calcd for C27H39Ce: Ce, 27.81.
Found: Ce, 27.4.
Synthesis of (C5Me4H)3Pr, 5. Following the procedure for 4,
PrCl3 (402 mg, 1.63 mmol) and KC5Me4H (766 mg, 4.84 mmol)
1
gave a yellow powder. (0.640 g, 78%). H NMR (C6D6) δ -30.5
(18H, C5Me4H), 19.0 (18H, C5Me4H), 78.2 (3H, C5Me4H). 13C
NMR (C6D6) δ -49.3 (C5Me4H), 15.8 (C5Me4H), 251.3 (C5Me4H),
280.4 (C5Me4H), 328.8 (C5Me4H). Anal. Calcd for C27H39Pr: Pr,
27.93. Found: Pr, 27.6.
(11) Evans, W. J.; Perotti, J. M.; Kozimor, S. A.; Champagne, T. M.; Davis,
B. L.; Nyce, G. W.; Fujimoto, C. H.; Clark, T. D.; Johnston, M. A.;
Ziller, J. W. Organometallics 2005, 24, 2916.
(12) Evans, W. J.; Hughes, L. A.; Hanusa, T. P. J. Am. Chem. Soc. 1984,
106, 4270.
Synthesis of [(C5Me4H)2(THF)Ce]2(µ-η2:η2-N2), 6. In a glove-
box, complex 4 (68 mg, 0.13 mmol) was added to KC8 (20 mg,
0.15 mmol) in 10 mL of THF. The solution became red and was
allowed to stir for 3 h. The solution was centrifuged, and the solvent
was removed from the supernatant in vacuo to give dark red solids.
Toluene extraction, followed by centrifugation and removal of
solvent from the supernatant in vacuo, left a yellow-green oil.
Yellow crystals were obtained from toluene at -35 °C (45 mg,
71%). Complex 6 was obtained similarly from reaction of 4 and
(13) Bergbreiter, D. E.; Killough, J. M. J. Am. Chem. Soc. 1978, 100, 2126.
(14) Taylor, M. D.; Carter, C. P. J. Inorg. Nucl. Chem. 1962, 24, 387.
(15) Evans, W. J.; Rego, D. B.; Ziller, J. W. Inorg. Chem. 2006, 45, 3437.
(16) (a) Evans, D. F. J. Chem. Soc. 1959, 2003-2005. (b) Becconsal, J.
K. Mol. Phys. 1968, 15, 129-139. (c) Lide, D. R., Ed. CRC Handbook
of Chemistry and Physics, 72nd ed.; CRC Press: Boca Raton, FL,
1991-1992. (d) Shoemaker, D. P.; Garland, C. W.; Steinfeld, J. I.;
Nibler, J. W. Experiments in Physical Chemisty, 4th ed.; McGraw-
Hill, New York, 1981; p 402.
(17) (a) Buchanan, G. W.; Crutchley, R. J. Magn. Reson. Chem. 1994, 32,
552. (b) Levy, G. C.; Lichter, R. L. Nitrogen-15 Nuclear Magnetic
Resonance Spectroscopy; Wiley-Interscience: New York, 1979.
(18) Evans, W. J.; Johnston, M. A.; Clark, R. D.; Ziller, J. W. Inorg. Chem.
2000, 39, 3421.
1
either excess K or excess Na. H NMR (C7D8) δ -4.16, -0.31,
0.80, 1.63, 11.80. 13C NMR (C7D8) δ 0.9, 1.5, 14.2. 15N NMR
(20) Exponential line broadening at 10 Hz was used in the data processing.
(21) Schumann, H.; Glanz, M.; Hemling, H. J. Organomet. Chem. 1993,
445, C1.
(19) Evans, W. J.; Engerer, S. C.; Coleson, K. M. J. Am. Chem. Soc. 1981,
103, 6672.
(22) Schumann, H.; Glanz, M.; Hemling, H.; Hahn, F. E. Z. Anorg. Allg.
Chem. 1995, 621, 341.
Inorganic Chemistry, Vol. 45, No. 26, 2006 10791